depends upon costs and profits
Thermal aquaculture: engineering and economics Thermal
si inlet
Pipeline transferring fish to processingan& freering pleat
effluents from electric power plants have been a subject of increased environmental concern, and national power demands may double over the next decade. For every kilowatt of electrical energy generated, more than 1 and as high as 2 kW of low-grade thermal energy will be produced and discharged into water or air as a waste. This waste heat could be considered a resource and examined as to how it may be utilized productively. Very little has been done to demonstrate the value of this waste heat in biological applications, particularly in agriculture and aquaculture. Much has been published on the potential and possible limitations of utilizing thermal effluents to enhance the culture of aquatic species. Small-scale experiments have been described for shrimp and pompano in the United States, a variety of fin-fish in Great Britain, multispecies culture in Japan, and carp culture in the USSR. However, large-scale application of these effluents for aquaculture will be dependent on its commercial viability. (Figure 1 illustrates increasing demand.) Status of aquaculture
Aquaculture is a term that in recent times has come to imply a degree of environmental control over the culture medium such that fish yields are enhanced by orders of magnitude. Most impressive are the yields in running water culture with intensive feeding practiced by the Japanese-800,000 to 3 million lb/acre/year. By contrast, hunting wild species on U S . coastal waters by conventional gathering methods may yield only about 20 lb/acre/year. 232 Environmental Science & Technology
Shrimp consumption is expected to soar
The yield figures demonstrate the potential of aquaculture, but there are also problems. Aquaculture as a technology is still in its infancy. Intensive culture of marine fish species is generally confined to the warm months of the year. The population in culture is dependent on the natural nutrient concentration in drainage from rivers and estuaries. No universally suitable artificial food has been developed yet, and yields may be subject to drastic curtailment by predator attack when the facility is not isolated from the sea. The thermal discharge from a power plant is a potential source of warm water for maintaining optimum temperature ranges in aquatic environments for yearround fish culture and is a source of flowing water for intensive aquaculture. At large power stations of the 500-1000 MW size, flow volumes of hundreds of thousands of gallons per minute are available. Precedence for the use of thermal effluents in aquaculture is only of recent vintage. Mollusks such as oysters are currently being cultivated year round on a commercial scale by Long Island
Oyster Farms, Inc. (division of Inmont Corp.) using the coolant water of the Long Island Lighting Co. at Northport, L.I. Intake water, ranging from 40" to 70°F during the year, is warmed by 12" to 18°F and discharged a t the rate of 150,000 gpm into a 7-acre lagoon. A continual source of warm water permits year-round culture. Baby oysters from a controlled environmental hatchery are placed on trays, and racks of these trays are immersed into a discharge canal from four to six months. A "finishing" stage follows in which oysters are transplanted to cold water areas to mature. Overall, the growing period is cut in half from about five years under natural conditions to about 2.5 years under culture conditions. Catfish are being cultured commercially the year round at the fossil-fueled nnl.ler -Inn+ y",.*L
...-
feature
Aquaculture. Japanese shrimp, raised in warm wafer, may sell f o r $ I I - l 2 / l b Experimental and/or developmental work in thermal aquaculture includes the following projects: catfish culture at the Gallatin Power Plant of the Tennessee Valley Authority by Trans-Tennessee Industries, oyster culture a t Pacific Gas and Electric Plant in Humboldt Bay, and lobster culture at several institutions including a California group (San
b o n Gnr nnrl Flwtrir C n ~ and MariI1--..llylI ..-- n-._~_ . ....
+hnTorr. Flertrir '&nrir-
Co. at Lake Colorado City, Tex. Cages of catfish are put in effluent water in the plant discharge canal that is about 7075°F in the wintertime. Yields are reported to be the equivalent of 100 tons/ acrelyear with intensive feeding.
~
culture Research Corp.) and the Department of Sea and Shore Fisheries, the State of Maine. Florida Power Corp. and Ralston Purina Co. recently announced a joint five-year program to evaluate thermal effluents for the culVolume 6, Number 3, March 1972 233
ture of high-value aquatic species including shrimp. The Japanese have pioneered in the use of thermal effluents for aquaculture. Shrimp, eel, yellowtail, seabream, ayn, and whitefish are among the aquatic species that are being evaluated. Since 1964, at least six generating stations have established demonstration programs. In one reported experiment at a power plant in Matsuyama, shrimp cultured during the summer in controlled temperature ponds had a weight gain of 1.2 times that of shrimp cultured in ponds with no temperature control; in winter, growth as measured by weight gain was seven times that in ambient temperature water. The English commenced tests on the culture of plaice and sole on an experimental basis in 1966 using the thermal discharge from a nuclear plant in Scotland. With some temperature control and supplemental feeding, fish growth from the egg to a 1xi-lb size and above was attained in less than two years, which is less than half the time required in nature. Design a n d cost factors
Fish cultivation in a dynamic system could be a way to utilize a resource that is currently discarded as a waste from steam electric power plants. A flowing stream provides a culture system with a more uniform concentration of dissolved oxygen. Biological oxygen demand is minimized because fish wastes and excess foods are flushed away, and, the system is more responsive to temperature control. Only the Japanese have developed the technology of culturing shrimp (Penaew jupunicus) into a commercially viable operation. Extensive culture is practiced in numerous bays and inlet areas diked off from the sea, while intensive culture with flowing water has only recently been demonstrated. In the Gulf of Mexico, shrimp growth under natural conditions is limited to the time period between April or May to about October or November when the water temperature ranges from 70" to 85°F. Growth virtually ceases when the water temperature drops below 70°F and does not resume again until the next spring when the water temperature warms up. However, if warm water were available on a yearround basis, two crops instead of one might be produced annually (Figure 2). An increase in the temperature of the water environment from 68" to 78°F increases the growth rate by more than 234 Environmental Science & Technology
Figure 2
Shrimp normally yield one generationlyr,, but. .
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Time in channel culture (months) Shrimp growth in the Gulf of Mexico
80%, implying that better control of the water temperature might even produce three crops annually. A conceptual design is based on the shrimp growth curve but is equally applicable, in principle, to culturable finfish species. As in Japanese culture, a period of up to 60 days is allotted to hatchery growth where mass cultivation from the egg to shrimp fry is done under highly controlled conditions. At this stage, the shrimp population should be developed sufficiently to tolerate the rigor of channel culture with a greater than 90% survival rate. Continuous culture
For intensive culture of shrimp on a continuous basis, a channel is divided into 26 pens of constant width and increasing length (Figure 3). The surface area of the first pen is proportional to the area under the first segment of the growth curve at the stage where channel culture of shrimp commences. Each succeeding pen area is proportional to the corresponding area formed by a segment of the growth curve. Shrimp fry are introduced into the first pen of a channel and cultivated for a set period of time until they attain a
weight density (g/ft2)that is common t o each succeedingly large pen. They are then advanced to a second pen, and more fry are stocked in the first pen. Each succeeding week, shrimp are moved forward one pen until the end of the growth period in the 26th pen. They are now ready for harvest, the channel system is in equilibrium, and, ideally, it should be possible to harvest a uniformsized product, week after week. A dependable source of supply of shrimp fry is assumed, so that, in principle, the number of new young shrimp introduced into the channel system is the same as the number of mature shrimp being harvested. Flowing water is essential to the practice of intensive fish culture. The linear flow rate has to be high enough to sweep away fish wastes but low enough so that shrimp can maintain their position at the bottom of the channel with minimal expenditure of their food intake energy. The flow rate also has to be high enough to maintain temperature control of the water stream and to minimize atmospheric effects on heat loss. Weight density is also an important consideration. In the continuous type of operation proposed, there is quite an economic incentive to devise culture
procedures such as maintaining constant weight density throughout the culture period which will enhance yield per acre. Aeration is also included in the design so that fish population is not limited by the dissolved oxygen content of the water. Feed from an external source is assumed so that culture population is not dependent on the nutrient concentration in the water stream. In Japanese culture, specific feeds have been developed for the larval and the post-larval stages of shrimp development. Beyond these stages, low-value fishes constitute the main diet of the shrimp in channel culture. This is suitable for culture economics in Japan where, during the off-season, live species sell on the retail market for $8/lb or more. In the United States, however, premium quality shrimp might be priced at one third of this value. Lowvalue fish as feed would not be economic in a large-scale continuous culture operation except under unique circumstances, such as a fish processing plant located in the vicinity of the aquaculture facility. Cost analysis
A hypothetical integrated aquaculture facility that includes a hatchery operation, culture in channels to a marketable size, and a processing plant that
converts cultured shrimp to a raw headless frozen product is considered in a cost analysis. A conceptual design is proposed for a plant that is sized to distribute 1000 million gpd of water at 80°F through 17 culture channels in parallel flow. Electricity is furnished from a nearby power plant to drive pumps to blend ambient temperature water with thermal discharge water and to aerate channel water to maintain optimum culture conditions the year round. Power is also furnished for processing and freezing the cultured product. Yields are projected to be 10 million lbs annually when shrimp weight density can be maintained at 110 g/ft2 over a total water surface of 400 acres. Capital costs are divided up into land development costs which are variable according to the site chosen, and equipment costs which are fixed. The sitesensitive costs include a water conveyance system to the installation, culture channel construction, and a discharge system. Major capital items for the integrated facility include mechanical equipment to divide each channel into pens, utility and aeration equipment, instrumentation, hatchery, food pelletizing facility, dewatering and harvesting equipment, and shrimp processing and freezing equipment. The total capital cost for such a facility is estimated
W "best buy" CONDUCTIVITY METERS
It comes in a small package (this one is only 6 x 5 ~ 5inches) but you get big value. New Hach Conductivity Meter nears e l e c t r o n i c p e r f e c t i o n w i t h o u t being over-engineered and expensive. Easily outperforms comparable instruments costing double and more. New tungsten electrode dip cell includes automatic temperature compensation (from 0 to 100°C) and is housed in rugged plastic. Solid-state circuitry is used throughout. Shipped with specific conductance scale unless otherwise specified. Range can be expanded i n 5 steps from 0-2 t o 0-20,000 m i c r o m h o s / c m . Other o p t i o n a l meter scales a v a i l a b l e : m g / l , sodium c h l o ride: ohms/cm, specific resistance; grains/gallon, sodium chloride. Complete instruction manual includes scale conversion tables. Ideal for schools, industry, any laboratory where pure or process water is checked. Also makes an inexpensive spare instrument for high volume laboratories. Anyone can operate.
Figure 3
Effluent channel design is based on shrimp growth
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Volume 6, Number 3, March 1972 235
to be more than $47,OOO/acre (of which $27,00O/acre is for site development). Annual operating cost is estimated to be $0.80/lb of headless frozen shrimp. Shrimp feed accounts for 60Z of the cost, assuming that the food cost is $O.lO/lb and the food conversion ratio is 3 Ibs of dry feed fedjlb of wet meat produced. The remainder of the cost is associated with labor for cultivating and processing shrimp, utilities, processing materials, plant overhead, and contingencies. With this capital and operating cost schedule as a basis, a sensitivity analysis can be prepared to show the effects of site-sensitive costs, food conversion ratio, wage rate and labor productivity, price of product, and shrimp yield on annual production costs. This is a function of return on investment for an idealized capacity of 10 million lb/year. A standard case for this analysis is: site-sensitive cost of $27,00O/acre, a food cost of $O.lO/lb and a food conversion ratio of 3:1, a labor wage rate of $2.00/man-hr, and a labor productivity of 100,000 lb of fish handled/man-year. Annual investment costs include only recovery and return on investment and interest on working cauital for 90 days. Deureciation is taken over a 15-year period. (Taxes and insurance have been omitted since these items vary from site to site.) This approach can be used to indicate a range of conditions under which thermal aquaculture might be commercially viable as well as some conditions where such a venture might result in a deficit
Analysis ...IN DEPTH
Dissolved Oxygen. Conductivity, Temperature, Specific Ion, ORP, PH
The Hydrolab SURVEYOR is the complete field system for the direct, in-situ meawrement of dissolved oxygen, conductivity, pH, temperature, and ion activities w redox potentials in natural waters. Parameter data, fully temperaturecwreaed for immediate interpretation, are supplied continuously for any depth to which the sen501 packag is lowered. Applicable t o both freshwater and saltwater meawrement problems, the SURVEYOR h a a sewim depth of 100 meterr. SURVEYOR Operationalfeatures:
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instrument care for immunity to rain, spray, wet handling
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For more information about the Surveyor and other Hydrolab instruments, pleae contact: Jim Flynn HYDROLAB CORPORATION Box 9406 Austin, Texas 78766 15121454-8646 Circle MI. 21 on Readers' Service Card 2316 Environmental Science & Technology
I
for the business operation. One cost factor that was not included in this analysis is the potential expense of effluentwaste treatment at the facility. Primary and perhaps secondary treatment may be necessary before discharging the effluentto receiving waters. M a r k e t i n g and economics
The potential for thermal aquaculture can be examined both from an economic and from a marketing point of view. With a source of warm water to culture continuously,the unit cost of production can be reduced significantly below that of a seasonally cultured product. As an example, producing catfish seasonally in open ponds has been estimated to cost about $0.30/lb while culture in flowing water on a continuous basis has been projected to be $0.20/1b. Land availability, large inventory of thermal effluent, and easy access to electric power are attractive synergisms between a power plant site and intensive aquaculture. Nuclear power stations are required by law to have an exclusion area around the plant site. Since the operating utility has complete control over this area, which may be hundreds of acres. there should be a m d e land to build an integrated facility. Unit size of a new nuclear station would be at least 500 MW, and the coolant water requirement might be 615 million gpd if a water temperature rise of 20°F is specified. Thermal aquaculture will not be universally possible at all power plant sites. Site specific factors such as water qual-
Oysters. Long Island Lighfing Co.'s discharge canal is used as an oyster nursery
Now analyze oily water for less than 50 cents pea sample Fish. Heated discharge water can easily be diverted into tanks for fish farming
ity, single-unit or multiple-unit power stations, and plant shutdown and startup patterns would he factors in determining the feasibility of such an operation. For example, coolant water sources should not contain toxic quantities of trace metals. Or economic ways of removing objectional impurities must he available. Biocide residuals in the thermal effluent must be helow levels that would he toxic to aquatic species in culture. Provisions may have to be made to cope with unscheduled shutdowns, when sudden changes in coolant water temperature might adversely affect the entire crop of fish in culture. The cost of sewage treatment of fish wastes in the culture facility effluent may he an important factor in the economics of the degree of intensiveness of fish culture. Nuclear plant thermal effluents used for aquaculture must he taken before the stream is used as a diluent for any radioactivity discharged from the installation. These are some of the major factors that would determine the commercial viability of thermal aquaculture for a particular power plant site. Thermal aquaculture has a potential that remains to he demonstrated. Since thermal effluents are waste products of the utility companies, a regnlated-industry, technical feasibility may he only one of several considerations to he reckoned with to prove its commercial viability. Legal and regulatory hurdles on a federal, state, and local level and marketing considerations may also he equally important factors. Ultimately, site-oriented demonstration projects will have to show the revenue-producing potential of thermal aquaculture and the extent to which it can assist in helping to pay for the cost of dissipating waste heat from an electric power plant. The re-
source value of this waste might then be estimated, and a liability of the present might he turned into an asset of the future. Additional reading
"Chemurgy-For Better Environment and Profits," Proceedings of 32nd Annual Conference, Chemurgic Council, 350 Fifth Ave., New York, N.Y. 10001.1971. Proceedings of the Conference on Beneficial Uses of Thermal Discharges, Albany, N.Y., September 16-18,1970, p51. New York State Department of Environmental Conservation, Albany, N.Y., 1971. "Joint Venture Aims at Thermal Effluent Use,"Amer.FirhFarmei,Z (8). 19(1971). "The Catfish Industry-1971," Amer. Fish Farmer, 2 (4). 12 (March 1971).
Fram's new mini-lab provides on-the-spot oily water analysis of up to six samples-in less than 45 minutes. Equally imDortant, it mav be used bv a tecnnician ana reduces material cost to less than 50cents per sample. Old extraction methods rew i r e d lengthy laborarory procedures and cost from $10.00 t o $50.00 per sample t o analyze. Also, test results based on the extraction method could not be reproduced accurately.
William C . Yee is ?ask force leader in the U S . Atomic Energy Commission's Environmental Impact Reports Project at Oak Ridge National Laboratory. Dr. Yee has been engaged in waste utilization and wasre treatment work since 1959 and has obfained four parenrs in these fields. Prior to his present position, he spent three years invesrigating productive uses for waste heat from power generaring stations, not only in the technical sense, bnt also from the legal, regulatory, and product markeringpoints of uiew. The research in this article was sponsored by the U S . Atomic Energy Commission under confracfwith Union Carbide Corp.
Fram's Trace Oil Analysis Kit fits easily into a speoially designed two-suiter suitcase and weighs only 27 pounds. Optional heated centrifuge is packed in a separate case and weighs just 22 pounds. The kit is ideal for anyone discharging water into sewer or streams. For additional information on trace oil analysis, write Fram today.
circle Ne. 21 PI Readers' Senice Card Volume 6, Number 3, March 1972 237
